Clear cell sarcoma of the kidney

Clear cell sarcomas of the kidney (CCSK) are a rare mesenchymal renal tumor that account for ~5% of primary renal neoplasms in the pediatric population .

Epidemiology

Clear cell sarcoma of the kidney is the second most common primary malignant pediatric renal neoplasm after Wilms tumor, with an annual incidence of 20 cases in the United States .  The mean age of diagnosis is 3 years , although it is very rare before the age of 6 months . Males are noticed to be affected more with an M:F of 2:1 .

Clinical presentation

Clear cell sarcoma of the kidney usually presents with a palpable abdominal mass; with hematuria and bone pain (in cases of metastatic disease) being less common.

Pathology

The tumor appears as a large solid mass, usually unilateral and unifocal, replacing most of the kidney or centered in the medulla . The cut surface appears gelatinous due to the abundance of extracellular mucopolysaccharides. Hemorrhage and necrosis are frequent findings (70%) .

Histologically, nine subtypes have been described . Most of these, however, will show some of the classic features of the tumor microscopically, consisting of cords or nests of cells surrounded by delicate branching cellular fibrovascular septa akin to chicken wire.

Although the margins of the tumor appear well defined grossly, they demonstrate infiltration into adjacent renal parenchyma with entrapment of the tubules on high power field microscopy. The entrapped tubules may become extensively dilated, giving the apparent cysts seen on gross tumor inspection .

Radiographic features

CT

These tumors usually enhance heterogeneously and to a lesser extent than the adjacent kidney, with non-enhancing foci representing hemorrhage and necrosis . They often cross the midline. Calcification is uncommon .

MRI

Usually appears as:

• T1: low to intermediate signal
• T2: high signal with cystic areas 

Treatment and prognosis

Clear cell sarcoma of the kidney has a worse prognosis compared to Wilms tumors, especially in those younger than 12 months of age . The mainstay treatment is radical nephrectomy with lymph node dissection. Relapse rate is high (20-40% of patients) .

Due to their rarity, there is no standard treatment for clear cell sarcoma of the kidney. Treatment may consist of surgical resection, chemotherapy, and/or radiotherapy .

Differential diagnosis

The imaging appearances for clear cell sarcoma of the kidney are non-specific and can be very similar to other primary renal neoplasms, especially Wilms tumor which is much more common. Finding of bone metastasis could suggest clear cell sarcoma of the kidney rather than Wilms tumor .